RTMPdump 源代码分析 1： main()函数

===============================

rtmpdump 是一个用来处理 RTMP 流媒体的工具包，支持 rtmp://,rtmpt://,rtmpe://,rtmpte://,and rtmps:// 等。之前在学习RTMP协议的时候，发现没有讲它源代码的，只好自己分析，现在打算把自己学习的成果写出来，可能结果不一定都对，先暂且记录一下。

使用RTMPdump下载一个流媒体的大致流程是这样的：

RTMP_Init();//初始化结构体
InitSockets();//初始化Socket
RTMP_ParseURL();//解析输入URL
RTMP_SetupStream();//一些设置
fopen();//打开文件，准备写入
RTMP_Connect();//建立NetConnection
RTMP_ConnectStream()//建立NetStream
Download();//下载函数
RTMP_Close();//关闭连接
fclose();//关闭文件
CleanupSockets();//清理Socket

其中Download()主要是使用RTMP_Read()进行下载的。

注：可以参考：RTMP流媒体播放过程

下面贴上自己注释的RTMPDump源代码。注意以下几点：

1.此RTMPDump已经被移植进VC 2010 的 MFC的工程，所以main()函数已经被改名为rtmpdump()，而且参数也改了，传进来一个MFC窗口的句柄。不过功能没怎么改（控制台程序移植到MFC以后，main()就不是程序的入口了，所以main()名字改成什么是无所谓的）

2.里面有很多提取信息的代码形如：rtmp.dlg->AppendCInfo("开始初始化Socket...");这些代码是我为了获取RTMP信息而自己加的，并不影响程序的执行。

int rtmpdump(LPVOID lpParam,int argc,char **argv)
{
	
  extern char *optarg;
  //一定要设置，否则只能运行一次
  extern int optind;
  optind=0;
  int nStatus = RD_SUCCESS;
  double percent = 0;
  double duration = 0.0;

  int nSkipKeyFrames = DEF_SKIPFRM;	// skip this number of keyframes when resuming

  int bOverrideBufferTime = FALSE;	// if the user specifies a buffer time override this is true
  int bStdoutMode = TRUE;	// if true print the stream directly to stdout,messages go to stderr
  int bResume = FALSE;		// true in resume mode
  uint32_t dSeek = 0;		// seek position in resume mode,0 otherwise
  uint32_t bufferTime = DEF_BUFTIME;

  // meta header and initial frame for the resume mode (they are read from the file and compared with
  // the stream we are trying to continue
  char *metaHeader = 0;
  uint32_t nMetaHeaderSize = 0;

  // video keyframe for matching
  char *initialFrame = 0;
  uint32_t nInitialFrameSize = 0;
  int initialFrameType = 0;	// tye: audio or video

  AVal hostname = { 0,0 };
  AVal playpath = { 0,0 };
  AVal subscribepath = { 0,0 };
  int port = -1;
  int protocol = RTMP_PROTOCOL_UNDEFINED;
  int retries = 0;
  int bLiveStream = FALSE;	// 是直播流吗? then we can't seek/resume
  int bHashes = FALSE;		// display byte counters not hashes by default

  long int timeout = DEF_TIMEOUT;	// timeout connection after 120 seconds
  uint32_t dStartOffset = 0;	// 非直播流搜寻点seek position in non-live mode
  uint32_t dStopOffset = 0;
  RTMP rtmp = { 0 };

  AVal swfUrl = { 0,0 };
  AVal tcUrl = { 0,0 };
  AVal pageUrl = { 0,0 };
  AVal app = { 0,0 };
  AVal auth = { 0,0 };
  AVal swfHash = { 0,0 };
  uint32_t swfSize = 0;
  AVal flashVer = { 0,0 };
  AVal sockshost = { 0,0 };

#ifdef CRYPTO
  int swfAge = 30;	/* 30 days for SWF cache by default */
  int swfVfy = 0;
  unsigned char hash[RTMP_SWF_HASHLEN];
#endif

  char *flvFile = 0;

  signal(SIGINT,sigIntHandler);
  signal(SIGTERM,sigIntHandler);
#ifndef WIN32
  signal(SIGHUP,sigIntHandler);
  signal(SIGPIPE,sigIntHandler);
  signal(SIGQUIT,sigIntHandler);
#endif

  RTMP_debuglevel = RTMP_LOGINFO;

  //首先搜寻“ --quiet”选项
  int index = 0;
  while (index < argc)
    {
      if (strcmp(argv[index],"--quiet") == 0
	  || strcmp(argv[index],"-q") == 0)
	RTMP_debuglevel = RTMP_LOGCRIT;
      index++;
    }
#define RTMPDUMP_VERSION "1.0"
  RTMP_LogPrintf("RTMP流媒体下载 %sn",RTMPDUMP_VERSION);
  RTMP_LogPrintf
    ("2012 雷霄骅 中国传媒大学/信息工程学院/通信与信息系统/数字电视技术n");
  //RTMP_LogPrintf("输入 -h 获取命令选项n");
    RTMP_Init(&rtmp);
	//句柄-----------------------------
	rtmp.dlg=(CSpecialPRTMPDlg *)lpParam;
	//---------------------------------
	//----------------------
	rtmp.dlg->AppendCInfo("开始初始化Socket...");
	//-----------------------------
	if (!InitSockets())
	{
		//----------------------
		rtmp.dlg->AppendCInfo("初始化Socket失败！");
		//-----------------------------
		RTMP_Log(RTMP_LOGERROR,"Couldn't load sockets support on your platform,exiting!");
		return RD_FAILED;
	}
  //----------------------
  rtmp.dlg->AppendCInfo("成功初始化Socket");
  //-----------------------------
  /* sleep(30); */



  int opt;
/*  struct option longopts[] = {
    {"help",NULL,'h'},{"host",1,'n'},{"port",'c'},{"socks",'S'},{"protocol",'l'},{"playpath",'y'},{"playlist",'Y'},{"rtmp",'r'},{"swfUrl",'s'},{"tcUrl",'t'},{"pageUrl",'p'},{"app",'a'},{"auth",'u'},{"conn",'C'},#ifdef CRYPTO
    {"swfhash",'w'},{"swfsize",'x'},{"swfVfy",'W'},{"swfAge",'X'},#endif
    {"flashVer",'f'},{"live",'v'},{"flv",'o'},{"resume",'e'},{"timeout",'m'},{"buffer",'b'},{"skip",'k'},{"subscribe",'d'},{"start",'A'},{"stop",'B'},{"token",'T'},{"hashes",'#'},{"debug",'z'},{"quiet",'q'},{"verbose",'V'},{0,0}
  };*/
  //分析命令行参数，注意用法。
  //选项都是一个字母，后面有冒号的代表该选项还有相关参数
  //一直循环直到获取所有的opt
  while ((opt =
	  getopt/*_long*/(argc,argv,"hVveqzr:s:t:p:a:b:f:o:u:C:n:c:l:y:Ym:k:d:A:B:T:w:x:W:X:S:#"/*,longopts,NULL*/)) != -1)
    {
	//不同的选项做不同的处理
      switch (opt)
	{
	case 'h':
	  usage(argv[0]);
	  return RD_SUCCESS;
#ifdef CRYPTO
	case 'w':
	  {
	    int res = hex2bin(optarg,&swfHash.av_val);
	    if (res != RTMP_SWF_HASHLEN)
	      {
		swfHash.av_val = NULL;
		RTMP_Log(RTMP_LOGWARNING,"Couldn't parse swf hash hex string,not hexstring or not %d bytes,ignoring!",RTMP_SWF_HASHLEN);
	      }
	    swfHash.av_len = RTMP_SWF_HASHLEN;
	    break;
	  }
	case 'x':
	  {
	    int size = atoi(optarg);
	    if (size <= 0)
	      {
		RTMP_Log(RTMP_LOGERROR,"SWF Size must be at least 1,ignoringn");
	      }
	    else
	      {
		swfSize = size;
	      }
	    break;
	  }
        case 'W':
	  STR2AVAL(swfUrl,optarg);
	  swfVfy = 1;
          break;
        case 'X':
	  {
	    int num = atoi(optarg);
	    if (num < 0)
	      {
		RTMP_Log(RTMP_LOGERROR,"SWF Age must be non-negative,ignoringn");
	      }
	    else
	      {
		swfAge = num;
	      }
	  }
          break;
#endif
	case 'k':
	  nSkipKeyFrames = atoi(optarg);
	  if (nSkipKeyFrames < 0)
	    {
	      RTMP_Log(RTMP_LOGERROR,"Number of keyframes skipped must be greater or equal zero,using zero!");
	      nSkipKeyFrames = 0;
	    }
	  else
	    {
	      RTMP_Log(RTMP_LOGDEBUG,"Number of skipped key frames for resume: %d",nSkipKeyFrames);
	    }
	  break;
	case 'b':
	  {
	    int32_t bt = atol(optarg);
	    if (bt < 0)
	      {
		RTMP_Log(RTMP_LOGERROR,"Buffer time must be greater than zero,ignoring the specified value %d!",bt);
	      }
	    else
	      {
		bufferTime = bt;
		bOverrideBufferTime = TRUE;
	      }
	    break;
	  }
	//直播流
	case 'v':
		//----------------
		rtmp.dlg->AppendCInfo("该RTMP的URL是一个直播流");
		//----------------
	  bLiveStream = TRUE;	// no seeking or resuming possible!
	  break;
	case 'd':
	  STR2AVAL(subscribepath,optarg);
	  break;
	case 'n':
	  STR2AVAL(hostname,optarg);
	  break;
	case 'c':
	  port = atoi(optarg);
	  break;
	case 'l':
	  protocol = atoi(optarg);
	  if (protocol < RTMP_PROTOCOL_RTMP || protocol > RTMP_PROTOCOL_RTMPTS)
	    {
	      RTMP_Log(RTMP_LOGERROR,"Unknown protocol specified: %d",protocol);
	      return RD_FAILED;
	    }
	  break;
	case 'y':
	  STR2AVAL(playpath,optarg);
	  break;
	case 'Y':
	  RTMP_SetOpt(&rtmp,&av_playlist,(AVal *)&av_true);
	  break;
	  //路径参数-r
	case 'r':
	  {
	    AVal parsedHost,parsedApp,parsedPlaypath;
	    unsigned int parsedPort = 0;
	    int parsedProtocol = RTMP_PROTOCOL_UNDEFINED;
		//解析URL。注optarg指向参数（URL）
		RTMP_LogPrintf("RTMP URL : %sn",optarg);
		//----------------
		rtmp.dlg->AppendCInfo("解析RTMP的URL...");
		//----------------
	    if (!RTMP_ParseURL
		(optarg,&parsedProtocol,&parsedHost,&parsedPort,&parsedPlaypath,&parsedApp))
	      {
			//----------------
			rtmp.dlg->AppendCInfo("解析RTMP的URL失败！");
			//----------------
		RTMP_Log(RTMP_LOGWARNING,"无法解析 url (%s)!",optarg);
	      }
	    else
	      {
			//----------------
			rtmp.dlg->AppendCInfo("解析RTMP的URL成功");
			//----------------
		//把解析出来的数据赋值
		if (!hostname.av_len)
		  hostname = parsedHost;
		if (port == -1)
		  port = parsedPort;
		if (playpath.av_len == 0 && parsedPlaypath.av_len)
		  {
		    playpath = parsedPlaypath;
		  }
		if (protocol == RTMP_PROTOCOL_UNDEFINED)
		  protocol = parsedProtocol;
		if (app.av_len == 0 && parsedApp.av_len)
		  {
		    app = parsedApp;
		  }
	      }
		  break;
	  }
	case 's':
	  STR2AVAL(swfUrl,optarg);
	  break;
	case 't':
	  STR2AVAL(tcUrl,optarg);
	  break;
	case 'p':
	  STR2AVAL(pageUrl,optarg);
	  break;
	case 'a':
	  STR2AVAL(app,optarg);
	  break;
	case 'f':
	  STR2AVAL(flashVer,optarg);
	  break;
	//指定输出文件
	case 'o':
	  flvFile = optarg;
	  if (strcmp(flvFile,"-"))
	    bStdoutMode = FALSE;

	  break;
	case 'e':
	  bResume = TRUE;
	  break;
	case 'u':
	  STR2AVAL(auth,optarg);
	  break;
	case 'C': {
	  AVal av;
	  STR2AVAL(av,optarg);
	  if (!RTMP_SetOpt(&rtmp,&av_conn,&av))
	    {
	      RTMP_Log(RTMP_LOGERROR,"Invalid AMF parameter: %s",optarg);
	      return RD_FAILED;
	    }
	  }
	  break;
	case 'm':
	  timeout = atoi(optarg);
	  break;
	case 'A':
	  dStartOffset = (int) (atof(optarg) * 1000.0);
	  break;
	case 'B':
	  dStopOffset = (int) (atof(optarg) * 1000.0);
	  break;
	case 'T': {
	  AVal token;
	  STR2AVAL(token,optarg);
	  RTMP_SetOpt(&rtmp,&av_token,&token);
	  }
	  break;
	case '#':
	  bHashes = TRUE;
	  break;
	case 'q':
	  RTMP_debuglevel = RTMP_LOGCRIT;
	  break;
	case 'V':
	  RTMP_debuglevel = RTMP_LOGDEBUG;
	  break;
	case 'z':
	  RTMP_debuglevel = RTMP_LOGALL;
	  break;
	case 'S':
	  STR2AVAL(sockshost,optarg);
	  break;
	default:
	  RTMP_LogPrintf("unknown option: %cn",opt);
	  usage(argv[0]);
	  return RD_FAILED;
	  break;
	}
    }

  if (!hostname.av_len)
    {
      RTMP_Log(RTMP_LOGERROR,"您必须指定 主机名(hostname) (--host) 或 url (-r "rtmp://host[:port]/playpath") 包含 a hostname");
      return RD_FAILED;
    }
  if (playpath.av_len == 0)
    {
      RTMP_Log(RTMP_LOGERROR,"您必须指定 播放路径(playpath) (--playpath) 或 url (-r "rtmp://host[:port]/playpath") 包含 a playpath");
      return RD_FAILED;
    }

  if (protocol == RTMP_PROTOCOL_UNDEFINED)
    {
      RTMP_Log(RTMP_LOGWARNING,"您没有指定 协议(protocol) (--protocol) 或 rtmp url (-r),默认协议 RTMP");
      protocol = RTMP_PROTOCOL_RTMP;
    }
  if (port == -1)
    {
      RTMP_Log(RTMP_LOGWARNING,"您没有指定 端口(port) (--port) 或 rtmp url (-r),默认端口 1935");
      port = 0;
    }
  if (port == 0)
    {
      if (protocol & RTMP_FEATURE_SSL)
	port = 443;
      else if (protocol & RTMP_FEATURE_HTTP)
	port = 80;
      else
	port = 1935;
    }

  if (flvFile == 0)
    {
      RTMP_Log(RTMP_LOGWARNING,"请指定一个输出文件 (-o filename),using stdout");
      bStdoutMode = TRUE;
    }

  if (bStdoutMode && bResume)
    {
      RTMP_Log(RTMP_LOGWARNING,"Can't resume in stdout mode,ignoring --resume option");
      bResume = FALSE;
    }

  if (bLiveStream && bResume)
    {
      RTMP_Log(RTMP_LOGWARNING,"Can't resume live stream,ignoring --resume option");
      bResume = FALSE;
    }

#ifdef CRYPTO
  if (swfVfy)
    {
      if (RTMP_HashSWF(swfUrl.av_val,(unsigned int *)&swfSize,hash,swfAge) == 0)
        {
          swfHash.av_val = (char *)hash;
          swfHash.av_len = RTMP_SWF_HASHLEN;
        }
    }

  if (swfHash.av_len == 0 && swfSize > 0)
    {
      RTMP_Log(RTMP_LOGWARNING,"Ignoring SWF size,supply also the hash with --swfhash");
      swfSize = 0;
    }

  if (swfHash.av_len != 0 && swfSize == 0)
    {
      RTMP_Log(RTMP_LOGWARNING,"Ignoring SWF hash,supply also the swf size  with --swfsize");
      swfHash.av_len = 0;
      swfHash.av_val = NULL;
    }
#endif

  if (tcUrl.av_len == 0)
    {
      char str[512] = { 0 };

      tcUrl.av_len = snprintf(str,511,"%s://%.*s:%d/%.*s",RTMPProtocolStringsLower[protocol],hostname.av_len,hostname.av_val,port,app.av_len,app.av_val);
      tcUrl.av_val = (char *) malloc(tcUrl.av_len + 1);
      strcpy(tcUrl.av_val,str);
    }

  int first = 1;

  // User defined seek offset
  if (dStartOffset > 0)
    {
      //直播流
      if (bLiveStream)
	{
	  RTMP_Log(RTMP_LOGWARNING,"Can't seek in a live stream,ignoring --start option");
	  dStartOffset = 0;
	}
    }
  //----------------
  rtmp.dlg->AppendCInfo("开始初始化RTMP连接的参数...");
  //----------------
  //设置
  RTMP_SetupStream(&rtmp,protocol,&hostname,&sockshost,&playpath,&tcUrl,&swfUrl,&pageUrl,&app,&auth,&swfHash,swfSize,&flashVer,&subscribepath,dSeek,dStopOffset,bLiveStream,timeout);
  //此处设置参数-----------------
  rtmp.dlg->AppendCInfo("成功初始化RTMP连接的参数");
  //-----------------------------
  char *temp=(char *)malloc(MAX_URL_LENGTH);

  memcpy(temp,rtmp.Link.hostname.av_val,rtmp.Link.hostname.av_len);
  temp[rtmp.Link.hostname.av_len]='';
  rtmp.dlg->AppendB_R_L_Info("主机名",temp);

  itoa(rtmp.Link.port,temp,10);
  rtmp.dlg->AppendB_R_L_Info("端口号",temp);

  memcpy(temp,rtmp.Link.app.av_val,rtmp.Link.app.av_len);
  temp[rtmp.Link.app.av_len]='';
  rtmp.dlg->AppendB_R_L_Info("应用程序",rtmp.Link.playpath.av_val,rtmp.Link.playpath.av_len);
  temp[rtmp.Link.playpath.av_len]='';
  rtmp.dlg->AppendB_R_L_Info("路径",temp);


  //-----------------------------

  /* Try to keep the stream moving if it pauses on us */
  if (!bLiveStream && !(protocol & RTMP_FEATURE_HTTP))
    rtmp.Link.lFlags |= RTMP_LF_BUFX;

  off_t size = 0;

  // ok,我们必须获得timestamp of the last keyframe (only keyframes are seekable) / last audio frame (audio only streams)
  if (bResume)
    {
	//打开文件，输出的文件(Resume)
      nStatus =
	OpenResumeFile(flvFile,&file,&size,&metaHeader,&nMetaHeaderSize,&duration);
      if (nStatus == RD_FAILED)
	goto clean;

      if (!file)
	{
	  // file does not exist,so go back into normal mode
	  bResume = FALSE;	// we are back in fresh file mode (otherwise finalizing file won't be done)
	}
      else
	{
	//获取最后一个关键帧
	  nStatus = GetLastKeyframe(file,nSkipKeyFrames,&dSeek,&initialFrame,&initialFrameType,&nInitialFrameSize);
	  if (nStatus == RD_FAILED)
	    {
	      RTMP_Log(RTMP_LOGDEBUG,"Failed to get last keyframe.");
	      goto clean;
	    }

	  if (dSeek == 0)
	    {
	      RTMP_Log(RTMP_LOGDEBUG,"Last keyframe is first frame in stream,switching from resume to normal mode!");
	      bResume = FALSE;
	    }
	}
    }
  //如果输出文件不存在
  if (!file)
    {
      if (bStdoutMode)
	{
	//直接输出到stdout
	  file = stdout;
	  SET_BINMODE(file);
	}
      else
	{
	//打开一个文件
	//w+b 读写打开或建立一个二进制文件，允许读和写。
		//-----------------
		rtmp.dlg->AppendCInfo("创建输出文件...");
		//-----------------------------
	  file = fopen(flvFile,"w+b");
	  if (file == 0)
	    {
			//-----------------
			rtmp.dlg->AppendCInfo("创建输出文件失败！");
			//-----------------------------
	      RTMP_LogPrintf("Failed to open file! %sn",flvFile);
	      return RD_FAILED;
	    }
	  rtmp.dlg->AppendCInfo("成功创建输出文件");
	}
    }

#ifdef _DEBUG
  netstackdump = fopen("netstackdump","wb");
  netstackdump_read = fopen("netstackdump_read","wb");
#endif

  while (!RTMP_ctrlC)
    {
      RTMP_Log(RTMP_LOGDEBUG,"Setting buffer time to: %dms",bufferTime);
	  //设置Buffer时间
	  //-----------------
	  rtmp.dlg->AppendCInfo("设置缓冲(Buffer)的时间");
	  //-----------------------------
      RTMP_SetBufferMS(&rtmp,bufferTime);
	  //第一次执行
      if (first)
	{
	  first = 0;
	  RTMP_LogPrintf("开始建立连接！n");
	  //-----------------
	  rtmp.dlg->AppendCInfo("开始建立连接（NetConnection）...");
	  //-----------------------------
	  //建立连接(Connect)
	  if (!RTMP_Connect(&rtmp,NULL))
	    {
			//-----------------
			rtmp.dlg->AppendCInfo("建立连接（NetConnection）失败！");
			//-----------------------------
	      nStatus = RD_FAILED;
	      break;
	    }
	  //-----------------
	  rtmp.dlg->AppendCInfo("成功建立连接（NetConnection）");
	  //-----------------------------
	  //RTMP_Log(RTMP_LOGINFO,"已链接...");

	  // User defined seek offset
	  if (dStartOffset > 0)
	    {
	      // Don't need the start offset if resuming an existing file
	      if (bResume)
		{
		  RTMP_Log(RTMP_LOGWARNING,"Can't seek a resumed stream,ignoring --start option");
		  dStartOffset = 0;
		}
	      else
		{
		  dSeek = dStartOffset;
		}
	    }

	  // Calculate the length of the stream to still play
	  if (dStopOffset > 0)
	    {
	      // Quit if start seek is past required stop offset
	      if (dStopOffset <= dSeek)
		{
		  RTMP_LogPrintf("Already Completedn");
		  nStatus = RD_SUCCESS;
		  break;
		}
	    }
	  //创建流(Stream)（发送connect命令消息后处理传来的数据）
	  itoa(rtmp.m_inChunkSize,10);
	  rtmp.dlg->AppendB_R_Info("输入Chunk大小",temp);
	  itoa(rtmp.m_outChunkSize,10);
	  rtmp.dlg->AppendB_R_Info("输出Chunk大小",temp);
	  itoa(rtmp.m_stream_id,10);
	  rtmp.dlg->AppendB_R_Info("Stream ID",temp);
	  itoa(rtmp.m_nBufferMS,10);
	  rtmp.dlg->AppendB_R_Info("Buffer时长（ms）",temp);
	  itoa(rtmp.m_nServerBW,10);
	  rtmp.dlg->AppendB_R_Info("ServerBW",temp);
	  itoa(rtmp.m_nClientBW,10);
	  rtmp.dlg->AppendB_R_Info("ClientBW",temp);
	  itoa((int)rtmp.m_fEncoding,10);
	  rtmp.dlg->AppendB_R_Info("命令消息编码方法",temp);
	  itoa((int)rtmp.m_fDuration,10);
	  rtmp.dlg->AppendB_R_Info("时长（s）",temp);

	  rtmp.dlg->ShowBInfo();
	  free(temp);
	  //-----------------
	  rtmp.dlg->AppendCInfo("开始建立网络流（NetStream）");
	  //-----------------------------
	  if (!RTMP_ConnectStream(&rtmp,dSeek))
	    {
		//-----------------
		rtmp.dlg->AppendCInfo("建立网络流（NetStream）失败！");
		//-----------------
	      nStatus = RD_FAILED;
	      break;
	    }
	  //-----------------
	  rtmp.dlg->AppendCInfo("成功建立网络流（NetStream）！");
	  //-----------------
	}
      else
	{
	  nInitialFrameSize = 0;

          if (retries)
            {
	      RTMP_Log(RTMP_LOGERROR,"Failed to resume the streamnn");
	      if (!RTMP_IsTimedout(&rtmp))
	        nStatus = RD_FAILED;
	      else
	        nStatus = RD_INCOMPLETE;
	      break;
            }
	  RTMP_Log(RTMP_LOGINFO,"Connection timed out,trying to resume.nn");
          /* Did we already try pausing,and it still didn't work? */
          if (rtmp.m_pausing == 3)
            {
              /* Only one try at reconnecting... */
              retries = 1;
              dSeek = rtmp.m_pauseStamp;
              if (dStopOffset > 0)
                {
                  if (dStopOffset <= dSeek)
                    {
                      RTMP_LogPrintf("Already Completedn");
		      nStatus = RD_SUCCESS;
		      break;
                    }
                }
              if (!RTMP_ReconnectStream(&rtmp,dSeek))
                {
	          RTMP_Log(RTMP_LOGERROR,"Failed to resume the streamnn");
	          if (!RTMP_IsTimedout(&rtmp))
		    nStatus = RD_FAILED;
	          else
		    nStatus = RD_INCOMPLETE;
	          break;
                }
            }
	  else if (!RTMP_ToggleStream(&rtmp))
	    {
	      RTMP_Log(RTMP_LOGERROR,"Failed to resume the streamnn");
	      if (!RTMP_IsTimedout(&rtmp))
		nStatus = RD_FAILED;
	      else
		nStatus = RD_INCOMPLETE;
	      break;
	    }
	  bResume = TRUE;
	}
	//-----------------
	
	//-----------------
	rtmp.dlg->AppendCInfo("开始将媒体数据写入文件");
	//-----------------
	  //下载,写入文件
      nStatus = Download(&rtmp,file,duration,bResume,metaHeader,nMetaHeaderSize,initialFrame,initialFrameType,nInitialFrameSize,bStdoutMode,bHashes,bOverrideBufferTime,bufferTime,&percent);
      free(initialFrame);
      initialFrame = NULL;

      /* If we succeeded,we're done.
       */
      if (nStatus != RD_INCOMPLETE || !RTMP_IsTimedout(&rtmp) || bLiveStream)
	break;
    }
	//当下载完的时候
  if (nStatus == RD_SUCCESS)
    {
		//-----------------
		rtmp.dlg->AppendCInfo("写入文件完成");
		//-----------------
      RTMP_LogPrintf("Download completen");
    }
	//没下载完的时候
  else if (nStatus == RD_INCOMPLETE)
    {
		//-----------------
		rtmp.dlg->AppendCInfo("写入文件可能不完整");
		//-----------------
      RTMP_LogPrintf
	("Download may be incomplete (downloaded about %.2f%%),try resumingn",percent);
    }
  //后续清理工作
clean:
  //-----------------
  rtmp.dlg->AppendCInfo("关闭连接");
  //-----------------
  RTMP_Log(RTMP_LOGDEBUG,"Closing connection.n");
  RTMP_Close(&rtmp);
  rtmp.dlg->AppendCInfo("关闭文件");
  if (file != 0)
    fclose(file);
  rtmp.dlg->AppendCInfo("关闭Socket");
  CleanupSockets();

#ifdef _DEBUG
  if (netstackdump != 0)
    fclose(netstackdump);
  if (netstackdump_read != 0)
    fclose(netstackdump_read);
#endif
  return nStatus;
}

// 初始化 sockets
int
InitSockets()
{
#ifdef WIN32
  WORD version;
  WSADATA wsaData;

  version = MAKEWORD(1,1);
  return (WSAStartup(version,&wsaData) == 0);
#else
  return TRUE;
#endif
}

inline void
CleanupSockets()
{
#ifdef WIN32
  WSACleanup();
#endif
}

int
Download(RTMP * rtmp,// connected RTMP object
	 FILE * file,uint32_t dSeek,uint32_t dStopOffset,double duration,int bResume,char *metaHeader,uint32_t nMetaHeaderSize,char *initialFrame,int initialFrameType,uint32_t nInitialFrameSize,int nSkipKeyFrames,int bStdoutMode,int bLiveStream,int bHashes,int bOverrideBufferTime,uint32_t bufferTime,double *percent)	// percentage downloaded [out]
{
  int32_t now,lastUpdate;
  int bufferSize = 64 * 1024;
  char *buffer = (char *) malloc(bufferSize);
  int nRead = 0;

  //long ftell(FILE *stream);
  //返回当前文件指针
  RTMP_LogPrintf("开始下载！n");
  off_t size = ftello(file);
  unsigned long lastPercent = 0;
  //时间戳
  rtmp->m_read.timestamp = dSeek;

  *percent = 0.0;

  if (rtmp->m_read.timestamp)
    {
      RTMP_Log(RTMP_LOGDEBUG,"Continuing at TS: %d msn",rtmp->m_read.timestamp);
    }
  //是直播
  if (bLiveStream)
    {
      RTMP_LogPrintf("直播流n");
    }
  else
    {
      // print initial status
      // Workaround to exit with 0 if the file is fully (> 99.9%) downloaded
      if (duration > 0)
	{
	  if ((double) rtmp->m_read.timestamp >= (double) duration * 999.0)
	    {
	      RTMP_LogPrintf("Already Completed at: %.3f sec Duration=%.3f secn",(double) rtmp->m_read.timestamp / 1000.0,(double) duration / 1000.0);
	      return RD_SUCCESS;
	    }
	  else
	    {
	      *percent = ((double) rtmp->m_read.timestamp) / (duration * 1000.0) * 100.0;
	      *percent = ((double) (int) (*percent * 10.0)) / 10.0;
	      RTMP_LogPrintf("%s download at: %.3f kB / %.3f sec (%.1f%%)n",bResume ? "Resuming" : "Starting",(double) size / 1024.0,*percent);
	    }
	}
      else
	{
	  RTMP_LogPrintf("%s download at: %.3f kBn",(double) size / 1024.0);
	}
    }

  if (dStopOffset > 0)
    RTMP_LogPrintf("For duration: %.3f secn",(double) (dStopOffset - dSeek) / 1000.0);

  //各种设置参数到rtmp连接
  if (bResume && nInitialFrameSize > 0)
  rtmp->m_read.flags |= RTMP_READ_RESUME;
  rtmp->m_read.initialFrameType = initialFrameType;
  rtmp->m_read.nResumeTS = dSeek;
  rtmp->m_read.metaHeader = metaHeader;
  rtmp->m_read.initialFrame = initialFrame;
  rtmp->m_read.nMetaHeaderSize = nMetaHeaderSize;
  rtmp->m_read.nInitialFrameSize = nInitialFrameSize;

  now = RTMP_GetTime();
  lastUpdate = now - 1000;
  do
    {
	//从rtmp中把bufferSize（64k）个数据读入buffer
      nRead = RTMP_Read(rtmp,buffer,bufferSize);
      //RTMP_LogPrintf("nRead: %dn",nRead);
      if (nRead > 0)
	{
	//函数：size_t fwrite(const void* buffer,size_t size,size_t count,FILE* stream);
	//向文件读入写入一个数据块。返回值：返回实际写入的数据块数目
	//（1）buffer：是一个指针，对fwrite来说，是要输出数据的地址。
	//（2）size：要写入内容的单字节数； 　　
	//（3）count:要进行写入size字节的数据项的个数； 　　
	//（4）stream:目标文件指针。 　　
	//（5）返回实际写入的数据项个数count。
	//关键。把buffer里面的数据写成文件
		if (fwrite(buffer,sizeof(unsigned char),nRead,file) !=
	      (size_t) nRead)
	    {
	      RTMP_Log(RTMP_LOGERROR,"%s: Failed writing,exiting!",__FUNCTION__);
	      free(buffer);
	      return RD_FAILED;
	    }
		//记录已经写入的字节数
	  size += nRead;

	  //RTMP_LogPrintf("write %dbytes (%.1f kB)n",nRead/1024.0);
	  if (duration <= 0)	// if duration unknown try to get it from the stream (onMetaData)
	    duration = RTMP_GetDuration(rtmp);

	  if (duration > 0)
	    {
	      // make sure we claim to have enough buffer time!
	      if (!bOverrideBufferTime && bufferTime < (duration * 1000.0))
		{
		  bufferTime = (uint32_t) (duration * 1000.0) + 5000;	// 再加5s以确保buffertime足够长

		  RTMP_Log(RTMP_LOGDEBUG,"Detected that buffer time is less than duration,resetting to: %dms",bufferTime);
		  //重设Buffer长度
		  RTMP_SetBufferMS(rtmp,bufferTime);
		  //给服务器发送UserControl消息通知Buffer改变
		  RTMP_UpdateBufferMS(rtmp);
		}
		  //计算百分比
	      *percent = ((double) rtmp->m_read.timestamp) / (duration * 1000.0) * 100.0;
	      *percent = ((double) (int) (*percent * 10.0)) / 10.0;
	      if (bHashes)
		{
		  if (lastPercent + 1 <= *percent)
		    {
		      RTMP_LogStatus("#");
		      lastPercent = (unsigned long) *percent;
		    }
		}
	      else
		{
			//设置显示数据的更新间隔200ms
		  now = RTMP_GetTime();
		  if (abs(now - lastUpdate) > 200)
		    {
		      RTMP_LogStatus("r%.3f kB / %.2f sec (%.1f%%)",(double) (rtmp->m_read.timestamp) / 1000.0,*percent);
		      lastUpdate = now;
		    }
		}
	    }
	  else
	    {
		//现在距离开机的毫秒数
	      now = RTMP_GetTime();
		  //每间隔200ms刷新一次数据
	      if (abs(now - lastUpdate) > 200)
		{
		  if (bHashes)
		    RTMP_LogStatus("#");
		  else
			//size为已写入文件的字节数
		    RTMP_LogStatus("r%.3f kB / %.2f sec",(double) (rtmp->m_read.timestamp) / 1000.0);
		  lastUpdate = now;
		}
	    }
	}
#ifdef _DEBUG
      else
	{
	  RTMP_Log(RTMP_LOGDEBUG,"zero read!");
	}
#endif

    }
  while (!RTMP_ctrlC && nRead > -1 && RTMP_IsConnected(rtmp) && !RTMP_IsTimedout(rtmp));
  free(buffer);
  if (nRead < 0)
	//nRead是读取情况
    nRead = rtmp->m_read.status;

  /* Final status update */
  if (!bHashes)
    {
      if (duration > 0)
	{
	  *percent = ((double) rtmp->m_read.timestamp) / (duration * 1000.0) * 100.0;
	  *percent = ((double) (int) (*percent * 10.0)) / 10.0;
	  //输出
	  RTMP_LogStatus("r%.3f kB / %.2f sec (%.1f%%)",*percent);
	}
      else
	{
	  RTMP_LogStatus("r%.3f kB / %.2f sec",(double) (rtmp->m_read.timestamp) / 1000.0);
	}
    }

  RTMP_Log(RTMP_LOGDEBUG,"RTMP_Read returned: %d",nRead);
  //读取错误
  if (bResume && nRead == -2)
    {
      RTMP_LogPrintf("Couldn't resume FLV file,try --skip %dnn",nSkipKeyFrames + 1);
      return RD_FAILED;
    }
  //读取正确
  if (nRead == -3)
    return RD_SUCCESS;
  //没读完...
  if ((duration > 0 && *percent < 99.9) || RTMP_ctrlC || nRead < 0
      || RTMP_IsTimedout(rtmp))
    {
      return RD_INCOMPLETE;
    }

  return RD_SUCCESS;
}

以上内容是我能理解到的rtmpdump.c里面的内容。

rtmpdump源代码（Linux）：http://download.csdn.net/detail/leixiaohua1020/6376561

rtmpdump源代码（VC 2005 工程）：http://download.csdn.net/detail/leixiaohua1020/6563163